Generally, there have been the following defects in metal, focal plane shutters for cameras of the type in which a group of opening (leading) and closing (trailing) blades are actuated sequentially to first open and then close the aperture to effect an exposure.
Firstly, it is difficult to adapt a shutter of this kind to miniaturized cameras because the space required for folding a group of shutter blades tends to increase the size of the shutter. As a means of eliminating this defect, it has been proposed to reduce the size of the space required for a group of shutter blades through a minute division of the shutter blades or by making the shutter blade smaller. However, the former method creates defects in that the blocking of light rays become deficient as the division of the blades is increased and also that actuation of the blades become more difficult, thereby causing exposure inaccuracy. Moreover, the durability of the shutter is impaired because a group of shutter blades is subject to increased inertia. The latter method creates a defect in that the blocking of light rays becomes deficient because of a decrease in the amount the blades are overlapped when they cover the aperture.
Secondly, such shutters have the defect that they are heavy in operation when being set and lack durability since a more powerful driving force is required to actuate a group of shutter blades with a large mass of inertia.
Thirdly, when the shutter blades are moved at high velocity in order to obtain a short exposure time or when synchronizing the shutter with a speed light, a group of closing blades may rebound from closed position so as partially to open the aperture and thus cause a reexposure after completion of the exposure actuation.